1. Field of the Invention
The present invention relates to a system and method for the detection of a transmitter unit in the proximity of a receiver system. More specifically, the present invention relates to a system that detects the proximity of a person carrying the transmitter to a dangerous machine configured with the receiver system, and determines if that person is close enough to be in danger.
2. Description of Prior Art
Industrial machines may be necessarily large and powerful. For example, continuous mining machines may be 40 feet long, 10-12 feet wide, 3-4 feet tall, and weigh 40 tons. Such machines have injured or killed people while being operated. For example, in “tramming,” a continuous mining machine mounted on tracks is moved from one location to another in confined spaces at relatively high speeds and can turn or change directions fast enough to pin an operator against a rib (i.e., wall) of the mining space.
With respect to the environment, it is may not be possible to set up traditional operator protection systems, such as light fences or guard rails, because the environment is generally unstructured (e.g., mining machines create the environment as they operate). Further, such environments are often noisy, dusty and wet.
A transducer, speaker or microphone that is exposed to such an environment is not likely to survive or function properly. For example, sonar and laser time-of-flight sensors exposed to such an environment will become dirty and non-operational very quickly. Further, such sensors have difficulty distinguishing between a people and other structural components in the environment, such as the wall of the mining space.
With respect to radio time-of-flight sensors, such as radar, while the components may be more durable in the environment the relatively short distances (e.g., two feet to 50 feet) between the operator and the machine make such sensors impractical and unreliable. Further, the requirement of a relatively large radio dish or directional radio antenna is impractical.
Alternatively, other systems utilize a magnetic field generator on the machine and a magnetic field sensor carried by the operator. The magnetic field generator creates a magnetic field around the machine. The magnetic field sensor senses the strength of the magnetic field and then relays the strength of the filed by radio back to the machine. If the operator is determined to be too close to the machine, the machine is shut down. However, this system is limited to a substantially circular safety perimeter around the machine, so there is no ability to arbitrarily define a safety perimeter because there is no way to determine an exact location of the operator with respect to the machine. Thus, the safety perimeter must be set to a radius that includes a safety margin from the most distant points of concern of the machine, leaving areas that are safe inside of the safety perimeter. This becomes a nuisance because it prevents the operator from operating in areas that are safe and effective because of the lack of geometric control of the safety perimeter.
What is needed is a system that can determine the location of the operator with respect to the machine and, if necessary, shut the machine down without requiring any structure in the environment. Advantageously, with such a system, the operator will learn to maintain a safe distance from the machine to be efficient in their job.